Hydraulic control system



Jun 16, 1942. w. A. TRA-UT 2,286,880

HYDRAULIC CONTROL SYSTEM :Ill

INVETOR 36 ATTORNEY@ June 16, 1942. w A. TRAUT HYDRAULIC vCONTROL SYSTEM 4 Sheeis---Sheejl 2 Filed July 5, 1940 -zzufmgw' 2 ATTORNEY.

June 16, 1942.. v w, A TRAUT 2,286,880

HYDRAULIC CONTROL SYSTEM y Filed J uly 5, 1940 4 Sheets-,Sheet 3 June 16, 1942. w. A. -rRAuT 2,286,880

- HYDRAULIC CONTROL SYSTEM Filed July 5, 1940 4 ShebS-Sheet 4 l sive pressure.

Patented June 16, 1942 HYDRAULIC coN'raoL SYSTEM william A. Trent, west Allis, wie., assigner te Blackhawk Mfg. Co., Milwaukee, Wis., a corporation of Wisconsin Application July 5, 1940, serial Ne. 344,091

(cl. so- 52) 16 Claims.

The present invention relates in general to improvements in the art of hydraulics, and relates more speciiically to improvements in the con-A struction and operation of hydraulic control systems for controlling the delivery of liquid from a pressure source to a pressure actuated device, and from the device back to the source.

An object'of my invention is to provide an improved hydraulic control system which is relatively simple in construction, readily manipulable,

and'highly eiiicient in operation. e

Many different types of hydraulic systems for controlling the delivery of liquid under pressure y from a pressure source such as a pump to devices such as Arams or jacks, and for releasing the to the source, have heretofore been proposed and used successfully in cases where the liquid was transferred and utilized at relatively low pressure. When high pressure was required, considerable difdculty has -invariably been encountered in transferring the liquid at the desired pressure from the pump to the ram, in maintaining the pressure at the ram, and in releasing the pressure; andwhile the prior high pressure hydraulic control systems may have been able to meet certain rather specific conditions of operation, they were not sumcientlyiiexible and reliable to meet many other desirable operating conditions. Most of these prior high pressure hydraulic controls were dimcult to actuate, were not entirely automatic in operation after being initially actuated,

introduced excessive leakage and thus failed to maintain the desired pressures, were too complicated and. therefore required considerable attention to maintain the same in operative condition, and were also insulciently flexible to perl mit use thereof f or diverse purposes.

It is therefore a more specific object Aof, my

invention to provide an improved high pressure tem whichv is extremely ilexible in its adaptations,

l5 pressure at the devices and returning the liquid einciency, especially in displacing the relatively movable elements of one or more single or double acting hydraulic jacks or rams. y

An additional specicl object of my present invention is to provide an improved hydraulic control assemblage which is highly eilcient in' use, and whereinrelatively simple and easily machinable valve actuating parts and standard ball valves may be utilized to eiiectively control the flow of liquid under extremelyA high pressure.

Another-additional object of the invention is to provide a high pressure hydraulic control mechanismwhich can be manufactured and sold at moderate cost, all parts of which'are readily accessible for inspection and adjustmenaand which can be utilized for many purposes. l

These and otherspecific objects and advantages of my invention will be apparent from the following detailed description.

A clear conception of the specic construction and of the mode of operating my improved system in conjunction with several types of pressure utilizing devices, may be had by referring te the 'anism inactive.

Fig. 2 is a similar diagram showing the system of Fig. l in action, with the pump operating and one of the manually operable selectors displaced to release high pressure liquid from the ram displacement chamber;

Fig. 3 is another similar diagram depicting the system of Fig. 1 in action, with the pump still operating and the other selector displaced to admit hydraulic pressure to the ram displacement chamber;

Fig. 4 is a draulic control system applied; toone double acting jack or ram, with all valves closed and the mechanism' in neutral position;

Fig. 5 is a diagram similar to that of Fig. 4,'

" l but illustrating the system in action with the and vwhich can be used to control delivery of,

actuating uid both to and from one or more high. pressure zones, without subjecting the manually manipulable actuating mechanism to excesmaybe utilized to perform work with maximum pump operating and one of the manual selectors shifted to release pressure liquid from onedisplacement chamber while admitting high pressure liquid to the other; e e

Fig. 6 is another diagram similar to that of Figs. 4 and 5, again showing the systemfin action but with the other selector shifted so as to reverse the Jack action e Fig. v'l is still another similar diagram illusmechanism in neutral or inactive position; and

diagram showing the improved hyn KFig. 8 is a somewhat enlarged longitudinal central section through one of the improved manually manipulable selector mechanisms.

While the improved hydraulic control system has been shown herein more or less diagrammatically and as cooperating with a reciprocating pump constituting the high pressure source, and with a jack or ram constituting the work performable under high pressure, it is not my desire or intent to thereby unnecessarily limit or restrict the scope or utility of the invention which may be utilized for diverse other purposes. Referring to the diagrams of Figs. l, 2 and 3, the improved high pressure control system shown therein, comprises in general, a. liquid pressure source or reciprocating single acting pump I9; a high pressure liquid operable device or single acting hydraulic ram II having a cylinder I2, a piston I3 reciprocable in the cylinder I2, and a displacement chamber I4 interposed between the cylinder and piston; a two-part reservoir I5 adapted to receive liquid discharged from the ram II, and to also receive excess liquid dischargedby the pump I9; means forming a pair of suction or inlet conduits I6 leading from the two sections of the reservoir I5 to the pump suction valve I1; a pair of similar manually operable selector mechanisms I8, I8 interposed, one in each of the suction conduits I6; means forming a pair of similar high pressure liquid discharge conduits I9, I9' connected at their inlet ends to a common passage 29 leading to be provided with a hole 43 adapted for attachment of a remote control cable. The medial portion of each piston 33 has a conical or tapered portion 44 which is adapted to coact with the extreme end o! the adjacent valve actuating rod 29, and each of these rods has an enlarged portion 45 snugly fitting and slidable in a bore 46 and provided with an annular groove 4.1 and small through passages 48, and also has a reduced portion 4'9 also snugly fitting its guide bore and directly cooperable with the adjacent valve and being provided with a flat 59. The annular piston groove 41 is registerable with a port 5I communicating with the pump discharge passage 29, only momentarily4 when the corresponding rod 29 is shifted from one extreme position to the pump discharge valve 2l, and interconnected intermediate their ends by ports 22, 23 which are connected to each other by a duct 24; a pair of v oppositely seating valves 25, 26 preferably of the ball type disposed within each of the conduits I9, I9', and of which the valves 25 are subjected directly to the pump discharge pressure, while the valves 26 are seatable by spring pressure but are adapted to be unseated by liquid pressure operable pistons 21, 21' movable in bores 28 constituting parts of the conduits I9, I9'; reciprocable members or rods 29 formed either in one or two sections and` being operable by the selectors I8, I8 to unseat the valves 25 against the liquid and spring pressures acting thereon; a.

conduit 39 connecting the conduit I9 beyond the valve 26 therein with the ram displacement chamber I4; and another conduit 3l connecting the conduit I9 beyond the valve 26 therein with the reservoir I5. i

While various elements of the improved con- I trol system have been shown diagrammatically in Figs. 1, 2 and 3, for the sake of clearness, many of these elements maybe housed directly within a common casing 32 as illustrated.. in Fig. 8,

wherein one of the manually opera-ble selectors I8 is shown more in detail. Each of the selectors I8, I8', comprises a piston 33 slidable in a bore 34 in the casing 32, and normally adapted to cut-oft communication between the adjacent pump suction conduitV I6 and tle reservoir- I5,'

when the piston 33 is in neutral position as in Fig. 1, vso as to prevent liquid from owing to the pump. The piston 33 of each selector I 8, I8' is constantly urged toward neutral position by a tension spring 35,.'and has an internal a' tuating stem 36 provided with. a guide member` 31 and extendingv outwardly -through a packing -38 carried by a closure fitting 39 for the adjacent bore 34. The outer end of eachselector actuating stem 36 isv provided with a head 49 having a side notch cooperable with a pin 4I carried by an actuating lever 42, and the head 49 may also port.

length that it will establish communication between the adjacent conduit I9, I9' and bore 46 only when the corresponding valve 25 is closed, and these :flats 59 serve to release liquid pressure fromthe portions "of the conduits I9, I9' beneath the pistons 21, 21' when these pistons are in lowermost position. The ball-valves 25 are urged toward closed position by springs 52, and the guide member 31 of each selector I8, I8 has an opening 53 therethrough for equalizing the pressures thereon, while each piston 33 is provided with drain holes 54 permitting escape of liquid to the conduits I6 or to the reservoir I6. It is to be noted, that the flats 59, passages 49, grooves 41, and ports 5I are of relatively small cross-sectional area, and that these ducts are so formed and positioned that they will quickly and eiectively prevent hydraulic locking of the movable elements of the system. iWhenever aselector I8, .I8' is returned to neutral ornormal position, the pump suction line I6 will be disconnected froxn the reservoir I5, vand the pump charge line 29, and since the suction is cut-off .before thecorresponding rod 29 can return to neutral, the residual liquid under pressure in the line 29 will escape to lthe reservoir I5 through the port 5I as the groove 41 moves past this When the rod hasv returned to normal, liquid under pressure trapped in the vconduit I9, I9' beneath the piston 21, 21', will also escape lo the reservoir I5 through the ilat 59passage 48, groove 41, bore 34, and port 54.

Each of the conduit bores 28 besides communicating with the adjacent valves 25, 26 and with each other through the ports 22, 23, has a liquid discharge duct 55 leading to the supply reservoir I5, and each piston 21,' 21 is provided with a medial groove 56 and with passages 51 connecting the groove 56 with the adjacent ball valve 26. The grooves 56 are adapted to register with the adjacent passages 55 when the corresponding pistons 21, 21' are active in opening the valves 26, and these valves besides being urged to closing position by liquid pressure from the pressure utilizing devices, are forced toward their seats by compression springs 58. The pistons 21, 21',

are not only.ad apted to control the ow of liquid through the passages 51, but also control the passage of liquid under high pressure through the ports 22, 23 and through the duct 24, so that these pistons should have. snugA coaction with the conduit bores 29.

During normal use of the system -when applied to a single acting ram Il as in Figs. 1, 2 and 3.

t 2,286,880 the apparatus when in neutrai position, has its' various elements positioned as illustrated in Fig. 1, with all of the valves 25, 26 seated, the pump delivery line 20 shut-off by the valves 25 and rods 29, and the selectors I8, I8' positioned so as to close communication between the suction conduits I6 and the reservoir I5. The displacement chamber I4 of the ram II may Acontainsome liquid, which is not, however, necessarily under pressure, but the valve 26 in the conduit I9 will be held closed by its spring 58, and the valve 26 in the conduit I9 will be vseated by its spring 59.

When the selector I8 is 'moved into the position shown in Fig, 2, the pump suction line I6 will be placed in communication with the reservoir I and liquid under pressure w'lll be delivered by the pump I0 through the passage 20, and past the valve 25 in the conduit I9, into the displacement chamber at the end of the corresponding piston 2l. The admission of high pressure liquid to the conduit I9 will displace the piston 2l therein and will cause this piston to unseat the corresponding ball valve 26, thereby permitting liquid to escape from the ram displacement chamber I6 through the conduit 36, passages 5'I and duct 55, to the reservoir I5, thereby permitting the piston of the ram II to move toward the right as shown in Fig. 2. The liquid under pressure delivered from the pump after elevating the piston 2l in the conduit I9, passes'through the port 22, duct 26 and port 23, into' the conduit i9 and elevates the other valve 26, thereby permitting the excess liquid under pressure to escape through the conduit 3i to the reservoir I5.

' This condition will prevail so long as the selector I6 is retained inthe position shown in Fig. 2, and when the actuating lever 42 for the selector i6 is released, the corresponding spring 35 `will promptly return the adjacent piston 33 to `neutral position as shown in Fig. l, thereby interrupting the delivery of liquid to and from the pump EIB. grooves el, flats 56 and ports 5i will then become quickly eiective to relieve the liquid pressure l from the conduit i6 and dischargeline 20.

The corresponding passages 68,v

When the other s'elector i6 is manipulated and positioned as shown in Fig. 3, while the pump i6v is operating, the valve 25 in the conduit i9' `will be unseated, thereby permitting the pump to draw liquid from the reservoir I5 and allowing liquid under pressure to flow from the pump discharge pipe 26 past the unseated valve 25, andy and causing this piston to positively. open the corresponding valve 26. Delivery of .liquid through the conduit 3l and through the duct 55 which communicate with the conduit I9', is then positively cut ou, .and high pressure liquid ows through the port 22, duct'25 and port 23, into the conduit i6, and unseats the valve 26 nearest to the ram. As this valve is unseat d, liquid undering lever t2 ofthe selector I6' is released, the

assemblage will again assume neutral position as shown in Fig. l.

It is to be. noted that the pump I6 should -be provided with the usual relief valve for permittingexcess liquid to escape to the reservoir I5 .into the conduit i9', thus moving the piston 2l'A the ram II have been positively stopped. After each return of the system to neutral position, the various passages 46, grooves 41 and dats 50 will permit liquid under pressure to escape from the conduits I9, I9' so that the system cannot become pressure bound or hydraulically locked, and will always be ready for immediate subsequent operation. It is lalso to be noted that when either of the selectors I8, I8 is manipulated, the subsequent functioning of the system is entirely automatic; and while the pump I0 may be operating constantly or may be started whenever a selector lI8, I8' is manipulated, it cannot deliver liquid underY pressure to the discharge line 26 unless .one of. the selectors is shifted, because these selectors cut-oi the suction or supply line when they are in neutral. position.

Referring more particularly to the diagrams of Figs. 4, 5 and 6, the improved high pressure hydraulic control system shown therein, is identical with that of Figs. 1, 2 and 3, but coacts with a dou-ble acting jack or ram 6I.. This double actin'g ram 6I has a cylinder 62, a piston or plunger connected to the other conduit I9' beyond the` piston 21 and ball valve 26 therein, by means of another conduit 66. It will thus be noted that while the conduit is similar to the conduit 36 of Fig. 1, the conduit 66 replaces the conduit 3l and there is no connection from the conduit I9' beyond the valve 26 therein, directly to thereservoir i5. Aside from these specic differences, the assemblage of Figs. 4, 5 and 6 may beA the same as that of Figs. l, 2 and' 3, and the selectors I8, I8' may be constructed as shown in detail in Fig. 8.

During normal use of the improved system when applied to a double acting ram 6I as in Figs.. 4, 5 and 6, the apparatus when in neutral position, has its various parts positioned as illustrated in Fig. 4, with al1l of the valves 25, 26'

the valves 25 will be maintained closed by the -When the pump i6 4is connected to the reservoir I5 and becomes active, by movement of the selector l5 into the position shown in 5, liquid under pressure will be delivered vfrom the pump through the passage` 26, and past the valve 25 in the conduit chamber at the end offthe corresponding piston 2l. The admission of high pressure liquid to the conduit I9 will displace the piston 2l' therein and.

y will cause this piston tounseat the correspondtoward the right. Simultaneously with this rewhen the various elements of the system and of .'75

ing ball valve 26, thereby permitting liquid to escape from the ram displacement chamber 69 through the conduit 65, passages 5l and duct 55, to the reservoir I5 as shown in Fig. 5, thus permitting the piston 63' ofthe ram.6l to -move lease of pressure from the ram displacement chamber 64, the liquid under pressure discharged i9, into the displacement.

from the pump I0, after. elevating the piston 21 in the conduit I9, ows through the port 22, duct 24 and port 23, into the conduit I9 where it lifts the other valve 26 from its seat, thereby permitting the high pressure liquid to flow through the pipe 66 and into the other dispiacement chamber 64 of the ram 6I. This admission of high pressure liquid to the displacement chamber 64 and release of pressure from the other displacement chamber 64, positivelymoves the piston 63 toward the right, and this movement will continue so long as the selector I8 is tions. If the selector I8 is manipulated, liquid retained in the position shown in Fig. 5. When the actuating lever 42 for the selector I8 is released, the corresponding vspring 35 will promptly return the piston 33 of this selector to neutral position as shown in Fig. 4, thereby cutting off the delivery of liquid from the pump I0.

When the other selector I8 is manipulated and positioned as shown in Fig. 6, during normal operation of the pump. I0, the valve 25 in the conduit I9 will be unseated, thereby permitting liquid under pressure to flow fromthe pump discharge pipe 20 past the unseated valve 25, and into the conduit I9 thus moving the piston 21' to a position wherein the corresponding valve 26 is positively opened. Delivery of liquid through the conduit 66 will thenbe cut oil and the ram displacement chamber 64 will be connected to the reservoir I5 through the conduit 66, passages 51, recess 56 and duct 55, thereby permitting the piston 63 to move toward the left. The lifting of the piston 21 simultaneously permits high pressure liquid to ow through the port 22, duct 24, and port 23 into the conduit I9, and to unseat the other valve 26 so that high pressure liquid will then be free to flow through the conduit 65 and' into the other displacement chamber 64. This admission of high pressure liquid to the displacement chamber 64, and release of the pressure from the displacement chamber 64', causes the piston 63 to move toward the left as viewed in Fig. 6, and this movement of the ram piston will continue as long as the pump I continues t0 operate and until the motion of the ram piston is positively arrested. When the operating lever for the selector I8 is released, the spring 35 will return this selector to neutral position as shown in Fig. 4, thereby arresting the movement of the ram piston.

Referring specifically to the modified assemblage of Fig. 7, the selector and control mechanisms are again the same as previously described, but the improvedhydraulic system is caused to cooperate with two single acting jacks or rams 1I, 1I', instead of with one single acting ram Il as in Fig. 1, or one-double acting ram 6I as in Fig. 4. The single acting ram 1I com.- prises a cylinder 12 having a piston 13 coacting with the cylinder bore and subjected to a displacement chamber 14, and the other single act- .ing ram 1I' comprises a cylinder 12 having therein a piston 13' subjected to a displacement chamber 14. The displacement chamber 14 is connected by a conduit 16 to the conduit I9 beyond the ball valve 26 therein, and the other dis- -placement chamber 14 is connected by another conduit I to the conduit I9 beyond the valve 26 therein. Aside from these differences, the aswill be-released from the displacement chamber 14 of the ram 1I tothe reservoir I5 through the conduit 15, duct 51, groove 56, and port 55, and

liquid under high pressure will be-simultaneously admitted from the pump I0 through the conduits I9, ports 22, 24, 23, past the right valve 26, and conduit 'I5'v to the displacement chamber 'I4' of the other ram 1I', thereby causing both of the pistons 13, 13- to simultaneously move toward the right as viewed in Fig. 7. If the other selector I8 is manipulated, liquid will be released from the displacement chamber 14' of the ram 1I' to the reservoir I5 through the conduit 15 duct 51, groove 56 and port v55, and liquid under high pressure will be simultaneously admitted from the pump I0 through the conduits I9', ports 22, 24, 23, past the left valve 26 and conduit 15 to the displacement chamber 14 of the other ram 1I to thereby cause both ram pistons 13, 13' to simultaneously move toward the left as viewed in Fig. '7. In this manner the two rams 1I, 1I' can be alternately actuated in opposite directions, and when the selectors I8, -I8' are released and return to neutral position, the pistons 21, 21 will return to neutral position and the valves 25, 26 will close. draulic system will again be automatically relieved as previously described, by the passages 48,

, grooves 41, hats 50, and ports 5| so as to prevent hydraulic locking.

From the foregoing detailed description it will be apparent that my present improvement provides an improved system for controlling' the flow of liquid under high pressure from a pressure source such as a pump I0, to and from a liquid operable device such as one or more rams Il, 6I, 1I, and comprising primarily a pair of conduits connecting the pressure source wi.h the device and oppositely seating valves in each conduit between which pressure operated pistons 21, 21 are disposed, these pistons being operable when the valves which are exposed to ythe pressure source are unseated. The improved' system is especially adapted for operation under high liquid pressure and the improved selectors are not subject to `undesirably high pressures and alge' therefore conveniently operable at all times, because the high liquid pressure in the system is automatically released whenever the lselectors are re- `turned to normal. The two independent selectors which are provided in the improved system,`

locking of the system. When the system is in neutral position, there is no pressure acting upon the rods 29 tending to oppose the movement of the selectors I8, I8,since it is impossible for the pump III to withdraw liquid frm the reservoir I5 and to create pressure until after one of the selectors has been actuaed. When single a'cting rams Il, 1I, 1I are utilized, the pistons may be moved in opposition to the pressure in the displacement chamber, with the usual springs or otherwise, andthe improved control system obviously possesses sufficient flexibiliy to permit its use in conjunction with either one single acting ram II, one double actingram 6I, or two single acting rams 1I. By duplicating the improved system, any number of either l.single acting vor The pressure from within this hydouble acting rams maybe controlled by any desirable number of selectors I8, i8-, and the various conduits, passages, pistons, and valves may be readily conned within compact casings 32 such as shown in Fig. 8. Any suitable control for starting the high pressure pump l when a selector lever 42 is operated, may be utilized, and the pump I0 may also be replaced by any other suitable source of liquid under high pressure,

while the'pressure operated devices'may assumeV various forms. The system is furthermore adapted for remote control, by virtue of the fact that selectors I8. i8 are not subject to excessive pressure resisting the normal operation thereof, and

the selector casings 32 may be readily machined andduplicated with the aid of jigs and are provided with removable plugs and other closures so as to permit convenient access to the valves, pistons, rods, springs, and other parts' of` the system.

Aside from the extreme flexibility in adaptation of the present system to rams and pressure operated devices of various types, the system is especially adapted for operation under high pressure by virtue of the use of primary and secondary ball valves 25, 26 respectively, for preventing escape of liquid under pressure. These ball valves.

pendent valve in each in a direction away from said source, a second are capable of tight closure, and the pistons 21,

in illustration, .and in actual practice only one' reservoir is required. The invention has proven highly successful in actual use, and besides being extremely efficient jin operation when subjected to liquid under high pressure, the system is also foolproof against hydraulic locking and can be utilized fordiverse purposes.

It should be understood that it is not desired to limit this invention to the exact details of constructionvor to the precise mode .of use, herein shown and described, for various vmodiiications Within the scope of the claims may occur to per-- sons skilled in the art.

1. A system lfor controlling the flow of liquid to' and from several liquid operable devices, said system comprising, a liquid supply reservoir, a

pump, means forming a conduit connecting said independent valve in each of said conduits seatable in a direction opposite to the direction of seating of 'the corresponding mst-mentionedvalve in said conduit, a selector for unseating each of said first-mentioned valves, and -a piston movable in each of said conduits by liquid under pressure passing said first-mentioned valve in the conduit for causing liquid under high pressure to open `the second valve in the other of said conduits.

3. A system for controlling the ow of liquid from a liquid operable device, said system comprising/means forming two conduits communicable with said device and each having .therein oppositely seating primary and secondary valves disposed at its opposite ends, an element movable in each of said conduits by liquid under pressure passing the corresponding primary valve to open the corresponding secondary 4valve and having liquid exhaust -passages communicating with said secondary valve, a selector for opening eachgof said primary valves, and a liquid passage connecting each of said conduits on one side of the movable' element therein with the other conduit on the other side of the movable element therein.

, 4. A system for controlling the flow of liquid froma pressure source to and from a liquid operable, device, said system comprising, a conduit connecting said source and said device, primary and secondary valves seating toward the opposite endsA of said c nduit an element movable in said conduit by liquid passing said primary valve to unseat said secondary valve, said element having an exhaust port therein, means cooperable with said element port when the element is moved for connecting said secondary valve to pump with said devices, a valve in said conduit movable during closing away from said pump, a second valve in said conduit movable during closing away from one of said devices, a manually actuable selector operable to open said lrstmentioned valve-.and to connectA the pump inlet to said reservoir, and a pressure actuated plungerv operable'by liquid under pressure passing said Yillrst valve to cause said liquid to open said second valve and thereby permit liquid under pressure to flow freely from said pump to said device, said plunger being formed to permit, other liquid to enter 'said reservoir fromanother of said devices.

2. A system for controlling the ow of liquid from a pressure source to and from 'a liquid op-v eralile device, said system comprising, means forming two interconnected conduits connecting sa'i'd Vpressure source with said device, an indeexhaust, means vfor opening said primary valve to admit liquid under pressure fromv the source to said element, and means for admitting liquid under pressure from the source to the device past said secondary valve when said primary valve is closed. I

' 5. A system for controlling'the ow of liquid,

'said system comprising, a liquid supply reservoir, a pump, a conduit having a valve therein normally exposed tothe discharge line of said pump,

a member movable to unseat said valveand having a restricted passage therein 'for relieving the pressure in said conduit when said valve is closed, and a selector operable to move said member to unseat said valve and to simultaneously connectv the suction line of said `pump to said reservoir.

6. A system for controlling the ilow of high pressure liquid from a pressure source to a liquid actuated device, said system comprising, a conduit connecting said source and said device and having a ball 'valve therein normally seated lby pressure from said source, a member movable to open said valve and having'passages therein for relieving the pressureiin said conduit when said valve` is closed, and a selector for moving said member and for admitting liquidto the presof said conduits seatablev moving said rod member to unseat said valve, said piston being formed to control the delivery of liquid to said source. y

8.. Ina hydraulic pressure control system, a pressure source, a liquid supply reservoir for said source, a device operable by liquid under pressure from said source, a conduit connecting said source-and said deviceand having primary and secondary oppositely seating valves therein, means for selectively operating said primary valve, a member movable by liquid under pressure passing said primary valve -to unseat said secondary valve, conduit means for returning liquid from said device to said reservoir and being controllable by said member, and other valve means for admitting liquid from said source to said device past said secondary valve when said primary valve is closed.

9. In a hydraulic vpressure control system, a pressure source, a liquid supply'reservoir for said source, a device operable by liquid under pressure from said source, aconduit connecting said source and said device and having a valve therein, a selector for opening said valve. and for connecting said source to said reservoir, and means interposed between said selector and said valve for releasing the pressure on both sides oi said valve when said selector is in neutral position.

l0. In a hydraulic system, a pump, a liquid supply reservoir, a device operable by liquid under pressure from said pump, a conduit connecting -said pump and said devicev and having a ball valve therein, a selector for opening saidvalve and for connecting the suction side of said pump with said reservoir, and means for relieving the discharge side of said pump and said valve from hydraulic pressure when said selector` is inactive.

1l. In a hydraulic system, a pump, a liquidsupply reservoir, a device operable by liquid under pressure fromsaid pump, a conduitconnecting said pump and said device and having a ball valve therein, a selector for opening said valve and for connecting the suction side of said pump with said reservoir, and means for simultaneously relieving the discharge side of said pump and said conduit on opposite sides of said valve from hydraulic pressure when said selector is inactive.

12. A system for controlling the ilow of liquid from a pressure source to and from a liquid operable device, said system comprising, a conduit connecting the source and the device, primary and secondary valves at the opposite'ends of said conduit and seating toward each other, an element movable in said conduit by liquid passing said primary valve to unseat said secondary valve, means operable by said movable element to connect said secondary valve to exhaust, means for opening said primary valve to admit liquid under pressure from said source to said movable element, and means for admitting liquid under pressure from the source to the device past said secondary valve when Vsaid primary valve is closed.

13. A system for controllng the iiow of liquid from a pressure source to and from a pair of liquid operable devices, said system comprising,

formed to co-operate with the corresponding secondary valve when unseated to exhaust liquid from the corresponding'device, a connection between said conduits and being co-operable with said movable means to admit liquid under pressure to the device which is not exhausting, and means for selectively operating said primary valves.

14. A system for controlling the iiow of liquid from a pressure source to and from a pair of Yliquid chambers, said system comprising, means forming two conduits connecting the source with the chambers and each having therein a primary and a secondary valve, a piston valve movable by liquid under pressure passing the primary valve in each of said conduits for unseating the secondary valve'in the same conduit, said piston valves being formed to co-operate with the corresponding secondary valve when unseated to exhaust liquid from the corresponding chamber, passages connecting said conduits and being cooperablek with said piston valves to admit liquid under pressure to the chamber which is not exhausting, and means for selectively operating said primary valves.

15. A system for controlling the flow of liquid from'a pressure source to a liquid operable device from a liquid supply, said system comprising,

means forming two conduits connecting iie source with the device and supply respectively, a primary valve in each .conduit near said source, a secondary valve in each conduit near said device and supply respectively, a third valve in each conduit movable by liquid under pressure passing the primary valve therein for unseating the secondary valve therein, passages connecting said conduits at said third valves, said third valve in the conduit communicating with said device being formed to exhaust liquid from said device when the secondary valve is unseated thereby and said third valve in the conduit communicating with said supply being formed to simultaneously permit liquid under pressure from said source to return to said supply past the secondary valve in said latter conduit when said device is exhausting, and means for selectively opening said priy mary valves.

16. A system for controlling the ilow of liquid from apressure source to a liquid operable device from a liquid supply, said system comprising, means forming two conduits connecting the source with the device and supply respectively, a primary valve in each conduit near said source, a secondary valve in each conduit near said device and supply respectively, a'third valve in each conduit movable by liquidunder pressure passing the primary valve vtherein for unseating the secondary valve therein, passagesl connecting said conduits at said third valves, said third valve in the conduit communicating with said supply being formed to deliver liquid from said source past the secondary valve in the other means forming two conduits connecting the source with the devices and each having therein a primary and a secondary valve, means movable in each of said conduits by liquid under pressure passing the primary valve therein for unseating the secondary valve therein, said means being WILLIAM A. TRAUT. 

